1. Field of the Invention
The present invention relates to an apparatus for conveying photosensitive material capable of conveying photosensitive material out of a paper magazine and sending it to a main processing unit such as a printer.
2. Description of the Related Art
A printer for printing images from negative film onto photographic paper or other such photosensitive material is installed with a paper magazine containing a roll of photosensitive material wound on a paper tube. The photosensitive material is drawn out of the paper magazine and cut to the desired size by a cutter, and the cut photosensitive material is conveyed to the printer to print images on the photosensitive material. After printing, the printed photosensitive material is sent from the printer to a developer for development.
A conveyance apparatus for drawing photosensitive material out of this type of paper magazine is taught by Japanese Unexamined Patent Publication No. 7(1995)-114108. This apparatus includes a set of drive rollers and opposing sets of nip rollers, both provided in the paper magazine. The photosensitive material is passed between the drive rollers and the nip rollers and the drive rollers are rotated by a driving power source installed in the main processing unit, typically a printer, to convey the photosensitive material as nipped between the drive rollers and the nip rollers.
The stability of photosensitive material conveyance can be enhanced by increasing the nipping force of the nip rollers on the photosensitive material. When the nipping force is set too high, however, the photosensitive material experiences pressure-fogging and nip-scratching. This has prompted the development of conveyance apparatuses that enhance the material conveyance stability by providing a pair of nip roller sets to enable the required nipping force to be applied to the photosensitive material as a whole even if the nipping force of the individual nip rollers is reduced. (The conveyance apparatus taught by Japanese Unexamined Patent Publication No. 7-114108, for example, enhances the conveyance stability of the photosensitive material by use of two sets of nip rollers.)
When the size of the photosensitive material to be used in a printer or other such processing apparatus is changed, the paper magazine has to be replaced with one loaded with photosensitive material of the new size. If this is done with the photosensitive material still drawn out of the paper magazine, the leading end of the photosensitive material will be exposed. Therefore, after the development or other processing of the photosensitive material has been completed, the set of drive rollers is driven in reverse to wind back the photosensitive material until its leading end is located inside the paper magazine. This prevents exposure of the leading end of the photosensitive material when the paper magazine is changed.
After the photosensitive material has been wound back into the paper magazine in this way, the leading end of the photosensitive material is kept in a nipped condition between the drive rollers and the nip rollers. FIGS. 7 and 8 respectively show how the leading end of the photosensitive material is held when only a single nip roller set is used and when a pair of nip roller sets are used. As shown, when only a single set of nip rollers is used, the leading end of the photosensitive material is maintained substantially straight but when two sets of nip rollers are used it is bowed between the two sets. This imparts undesirable curl to the leading end portion of the photosensitive material. When the photosensitive material imparted with such curl is conveyed, conveyance stability is liable to be degraded owing to jamming of the photosensitive material at conveyance rollers or some other portion of the main unit. Although this problem can be avoided by cutting off a narrow lateral strip from the leading end of the photosensitive material to remove the curl at the start of photosensitive material conveyance, this leads to another problem of paper fragments produced by the cutting being dispersed inside the main processing unit.